Crushed fingers, amputations, burns, blindness, these are all too common undesirable occurrences involving moving machinery. Eliminating the risk of such accidents is an integral part of the engineering design process, where risk assessment goes hand and hand with industry standards in order to provide adequate machine safeguards and protection to operators as well as bystanders.
Machine safeguards fall into three basic categories: Guards, Devices, and Distance.
Guards are physical barriers that are added to machines with the goal of keeping body parts, clothing, etc., separated from potentially hazardous areas. An example would be a metal cage surrounding drive belts and pulleys. Guards can also serve to keep material fragments and debris from flying out of machines while in operation, such as when an enclosure is built around the grinding wheel of a bench grinder.
Devices can consist of automatic controllers, often connected to sensors on machine componets. These controllers use a form of “safety interlock logic” to monitor the operating state of machinery. They must act quickly and automatically to stop the normal operation of a machine if they sense that an undesirable object, say a person’s forearm, is in danger of entering a hazardous area.
Controllers can be in the form of hard-wired electromechanical relays, embedded microprocessors, or programmable logic controllers (PLCs). Their sensors can include electrical switches embedded in floor mats or mounted on movable guards, incorporated into control handle grips, or linked to an access door latch. Still other sensors are more elaborate, using more sophisticated methods to maintain safety, such as photoelectric devices known as laser curtains. These act by spreading beams of light across an opening which may be a gateway to a dangerous area. If the beam is broken by an object, the controller takes appropriate action and renders the machinery inoperable.
Distance safeguards operate as you would infer them to, by designing machinery so that hazardous areas are kept a great enough distance from body parts, etc., so as to eliminate any danger of them being drawn into an unsafe area. An example of this factor at work would be when machinery is developed so that moving gears and other potential hazards are kept far out of the reach of someone by virtue of their overall design.
Sometimes even the best machine safeguard designs can be rendered ineffective after a piece of machinery is put into actual operation. The reasons for this are varied, from poor maintenance of equipment, to lack of training for operating personnel, to inadequate supervision of workers, or perhaps the machine has been modified to operate outside the parameters of its design capacity. Whatever the reason, people can be put at risk for serious injury and even death if machine safeguards are bypassed, eliminated, and defeated.
Archive for September, 2009
When you were a child, were you lucky enough to have someone who inspired you? Someone who filled you with the wonder and passion needed to pursue a fulfilling career? Was it a parent, a teacher, a friend? For me, it was my mother.
Mom grew up on a farm in west-central Wisconsin back in the 1930s. The Depression was on, and she and her siblings learned how to be resourceful at a young age. That’s how you survived in the days before rural electrification, high speed communication networks, interstate highways, big box stores, and many other things that we take for granted in the United States today.
When I was a kid back in the ’60s, my mom was the plumber, carpenter, mechanic, and general fix-it person of the family. No, my father wasn’t dead or absent, he just wasn’t handy, nor did he desire to be. Unlike many housewives, Mom didn’t call for professional help when the vacuum cleaner or washing machine was on the fritz. Instead she learned how they ticked, determined what she had to do to get them working again, then got busy fixing them herself. Whether it was a lack of money to pay a professional for their services or a genuine appreciation of the subject matter that motivated her, I don’t know. I just know that Mom, whether she realized it or not, approached technical challenges in our home much like a systems engineer. She had an eye for improving product design and used forensic engineering skills to get to the heart of her dead appliance’s problem.
Mom’s lack of formal technical training didn’t hold back her fix-its, and the basement workbench in our home was similar to a product development laboratory. As her apprentice on household repair projects, Mom would get me involved. It didn’t take long before I, too, understood how the timer in her washing machine made valves open and close, how the motor in her sewing machine made the needle move, how the toaster turned on and off, and how to fix a clock that wasn’t keeping time.
The education that my mother gave me formed a real world technical foundation for my future studies of engineering in college. Mom’s school gave me a practical understanding of the workings of machines and other devices that many of my classmates lacked. And the desire to keep things hands-on has stayed with me through my career, where the sanitary conditions of an office environment were often supplemented by activities that would continue to get my hands dirty.
I still love to take things apart, problem solve, and innovate. Thanks to Mom, I’m the engineer that I am today. My writing skills I had to pick up elsewhere…
Imagine being hit by a bolt of lightning. Like lightning, an arc flash can unexpectedly release tremendous amounts of energy, resulting in serious injuries and even death.
An arc flash is the result of a short circuit or electrical fault in energized equipment. Current flows through the air and creates an electrical arc, very much like the phenomenon of lightning. But unlike lightning, arc flash dangers are present in a myriad of circumstances that do not require storm conditions to manifest.
Over 80% of electrically related injuries involve some type of arc flash. They can be caused by a wide variety of factors, including: equipment malfunctions, inadequate safety procedures, carelessness, lack of training, dropped tools, etc. The amount of energy released by the electrical arc depends on the amount of electrical current flowing through the arc and how long the current will flow before it is interrupted by a circuit breaker or fuse.
The radiation released in an arc flash can be so intense and so rapid that it can instantly burn skin and ignite clothing. Temperatures at the electrical arc can rapidly climb to tens of thousands of degrees. At temps this extreme metal becomes liquid, then vaporizes, and the air surrounding the arc becomes superheated to approximately 30,000°F. The superheated air and metal vapor together expand with explosive force. This creates a dangerous and potentially lethal pressure wave of hot gas, molten metal droplets, and solid metal shards that can create burns and shrapnel wounds.
The Occupational Safety and Health Administration (OSHA) requires employers to assess the workplace for arc flash hazards that are present or that are likely to be present. Assessment is done using standards developed by the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers (IEEE) to specifically address arc flash hazards.
If hazards are identified, employers must mitigate risks by adhering to a six point compliance plan such as the following:
1. Implement a worker safety program with defined responsibilities.
2. Perform engineering studies that include calculations to determine the degree of arc flash hazards. These studies also must be updated when any changes to the electrical system are made by the employer or the electric utility.
3. Provide workers with the correct personal protective equipment (PPE) based on the study results. These PPE must then be maintained on site to protect workers.
4. Provide worker training on the hazards of arc flash. This training must be documented and workers must demonstrate proficiency through testing. Worker training must also be updated whenever any changes occur to the electrical system.
5. Provide appropriate tools for safe working.
6. Place conspicuous warning labels on equipment to warn workers about potential arc flash hazards.
OSHA, like other government agencies, expects employers to keep up with regulations and take the necessary steps to remain compliant. For example, OSHA won’t send notices out to employers to inform them that they must implement an arc flash program in their plant. It’s up to the employers to know that and institute the necessary precautions on their own.
It must also be noted that OSHA doesn’t walk employers through the steps of setting up an effective worker safety program. This means that workers can be exposed to arc flash hazards simply because their employer is ignorant of regulatory requirements and is operating based on misconceptions.
Some workers are unfortunate enough to work for employers that don’t take potential dangers like arc flash seriously enough to implement an effective safety program. When their wakeup call comes, it’s often too late.
Do you want to know more about implementing an effective Arc Flash Program in your facility? Phil O’Keefe developed and presents a 90-minute webinar entitled: “Arc Flash Program Fundamentals.” Contact him for more information about conducting this webinar for your organization.
Have you thought about using courtroom visual aids before but didn’t have a clue of where to begin?
Many feel that when they were born somehow the creativity bone was left out. As a result, they feel very unsure of themselves and are particularly doubtful about their ability to suggest to an artist what they might need. The difficulty that presents itself is not that they are unaware of what the real cause of the problem is, but rather unsure of how best to portray it to others, say a jury.
Those involved in the legal profession know that courtroom visual aids, a.k.a. courtroom demonstratives, can be effectively used to convey ideas that are easily lost in purely verbal descriptions. But should these be in the form of scale models? Annotated photos? Graphic art renditions? Computer Aided Design (CAD) drawings? No need to worry, this is the territory of the visual artist, well trained in perspective.
I recently received a call from an attorney client who was representing a worker who was severely injured in an industrial accident. The situation involved the operation of material handling equipment which was much too large to bring into the courtroom. And it was also far too complex to sufficiently depict its operation through the use of photographs or videotaping.
After gathering details about the accident, I determined that showing the jury a 1/20 scale model of the equipment as a whole would be the ideal way for the attorney to begin telling the story. This model would be used in conjunction with a much larger and fully operational 1/4 scale model of the key portion of the equipment that is held to have failed. This larger model would serve as a spotlight on the area in question, enabling the jury to zero in on specific details. And because it was fully operational, the attorney could demonstrate the precise sequence of events that led up to the injury. The jury might even be allowed to manipulate the mechanism themselves to gain an even better understanding.
In addition to these physical models, a graphic illustration would be used to illustrate the hazardous condition that existed immediately before the accident and how this led to the worker’s injuries. This final piece in the visual aid puzzle would serve to tie all the elements together.
No matter what the situation, a visual courtroom demonstrative can be devised to bring the situation at hand into graphic light, where its message can be easily absorbed by all.